One way fasteners are well known to those of ordinary skill in the art. Generally, these fasteners are constructed with features that allow a threaded shank portion of the fastener, usually a threaded screw type configuration, to pass through an orifice in one structure and ultimately “screw” into an adjacently positioned second structure until a head portion of the fastener engages the first structure. Once the head portion engages the first structure, the one way fastener is very difficult to remove due to diametrically opposed flat and convex portions that are configured to provide a recess that receives a screwdriver and allows the screwdriver to forcibly insert the fastener into the second structure when the screwdriver is rotated clockwise, but prevents the screwdriver from extracting the fastener when the screwdriver is rotated in a counter-clockwise direction.
Conventional one way fasteners are nothing more than a conventional rounded head screw with diametrically opposed quadrants machined flat. This rounded head feature contributes significantly to the problem of extracting a one way fastener. One way fasteners are very effective in preventing unauthorized persons or vandals from separating the fastener-joined structures. However, occasions do arise requiring the difficult task of removing one way fasteners.
Prior art extraction devices utilize features such as jaws to grasp the sides of the head of a fastener for removal. Examples of such devices are illustrated in U.S. Pat. Nos. 5,551,320 and 5,533,426. Unfortunately, these devices are of no use when there are no accessible sides to the fastener head.
Another prior art extraction device details a tool having a pair of “tips” for engaging a pair of tip receiving recesses in the head of the one way fastener. Such a device is depicted in U.S. Pat. No. 5,450,776 issued to the applicant. The device further includes a collar with asymmetrical radial serrations to grasp the periphery of the fastener head. This tip-recess and collar-head interaction provides the “foothold” necessary to maximize the effect of any rotational force applied to the fastener removal tool. This device is limited to extracting a specially designed fastener. The device cannot function optimally when a conventional fastener such as that described above is encountered.
In addition, U.S. Pat. No. 6,047,620, also issued to the present inventors and the entirety of which is incorporated herein by reference, discloses a tool for removing conventional one way fasteners. The device generally includes a collar and a shank that can be removably received by the collar, wherein in the shank is configured to engage complementary regions of the fastener head. The collar includes a recess having longitudinal ridges to engage perimeter portions of the fastener head. The shank and collar cooperate to provide additional rotational force to the fastener to thereby extract the fastener, whether the fastener is flush-mounted or counter-sunk. However, while these types of fasteners (with collars) are effective for their intended purpose, due to variations in the diameter of the fasteners, a collar may not fit over a certain fastener, and almost certainly not over multiple fasteners, each with differing head sizes.
Therefore, a need exists in the art for an adjustable fastener removal tool for extracting one way fasteners that can be adjusted to fit snuggly around a fastener. In addition, a need in the art exists for an adjustable fastener removal tool that is capable of extracting multiple differently sized one way fasteners.